I. Field of the Invention
The present invention relates generally to a microwave antenna and method for making the microwave antenna.
II. Description of Related Art
Dedicated short range radar communications (DSRC) of the type used in automotive vehicles occur at high microwave frequencies, currently about 77 gigahertz. Such DSRC systems are utilized not only for anti-collision systems, but also as well as other inter-vehicle and vehicle infrastructure communications. These previously known DSRC systems typically use microwave antenna arrays with a plurality of spaced apart horns for additional gain. Furthermore, since such antennas are utilized in automotive vehicles, a low cost antenna system is highly desirable.
One previously known method for constructing microwave horn antennas of the type used in automotive vehicles has been to place a layer of thermoplastic material in between two hot embossing plates so that one plate faces a front surface of the layer while a second plate faces the back side of the layer.
The first plate includes one or more horn shaped embossing elements while, similarly, the second embossing plate contains embossing elements corresponding in shape to the wave guide channels for the antenna. The embossing plates, when heated, are then compressed against the thermoplastic layer so that the horn shaped embossing elements penetrate the thermoplastic layer and ultimately abut against the second embossing plate. Similarly, the wave guide channel elements on the second embossing plate depress portions of the back side of the thermoplastic layer to form the wave guide channels so that the wave guide channels are interconnected with the one or more cones.
Thereafter, both the front and back sides of the wave guide are covered with metal by sputtering a metal both onto the cones as well as the wave guide channels. A metal plate is then positioned across the back side of the thermoplastic layer so that the wave guide channels are formed in between the metal plate and the metallized wave guide channels on the back side of the thermoplastic layer. The horn and wave guide channels are then further metal coated by electroplating.
A primary disadvantage of this previously known method of fabricating microwave horn antennas, however, is that a certain amount of plastic flash is formed at the intersection of the horn embossing element and the second embossing plate during the embossing process. Such plastic flash is not only difficult to metallize as required for proper antenna performance, but also interferes with the overall operation of the microwave antenna since the flash changes the ideal shape of the cone for optimal microwave performance.
In order to avoid degradation of antenna performance caused by the plastic flash, it has been the previous practice to remove the flash either with a knife or similar object prior to covering the horn with the metal coating. The removal of flash in this fashion, however, is imprecise and thus results in overall degradation of the performance for the antenna. Furthermore, this removal cannot be automated and requires manual handling, both of which increase the manufacturing cost.